Photophysical Properties of 4-Dicyanomethylene-2-methyl-6-(p-dimethylamino-styryl)-4H-pyran Revisited: Fluorescence versus Photoisomerization

Although 4-dicyanomethylene-2-methyl-6-(p-dimethylamino-styryl)-4H-pyran (DCM) has been known for many decades as a bright and photostable fluorophore, used for a wide variety of applications in chemistry, biology and physics, only little attention has been paid so far to the presence of multiple isomers and conformers, namely s-trans-(E), s-cis-(E), s-trans-(Z), and s-cis-(Z). In particular, light-induced E-Z isomerization plays a great role on the overall photophysical properties of DCM. Herein, we give a full description of a photoswitchable DCM derivative by a combination of structural, theoretical and spectroscopic methods. The main s-trans-(E) isomer is responsible for most of the fluorescence features, whereas the s-cis-(E) conformer only contributes marginally. The non-emitting Z isomers are generated in large conversion yields upon illumination with visible light (e.g., 485 or 514 nm) and converted back to the E forms by UV irradiation (e.g., 365 nm). Such photoswitching is efficient and reversible, with high fatigue resistance. The E→Z and Z→E photoisomerization quantum yields were determined in different solvents and at different irradiation wavelengths. Interestingly, the fluorescence and photoisomerization properties are strongly influenced by the solvent polarity: the fluorescence is predominant at higher polarity, whereas photoisomerization becomes more efficient at lower polarity. Intermediate medium (THF) represents an optimized situation with a good balance between these two features.

Enhanced cellular uptake efficiency of DCM probes or SN38 conjugating with phenylboronic acids

High-level of sialic acid (SA) expression on the surface of cancer cells is observed extremely common. Phenylboronic acids (PBAs) have a high affinity with SA. The cellular uptake efficiency could be enhanced by the strategy of introducing PBA fragments to the compounds. In this work, we synthesized five new probes with the Dicyanomethylene-4H-pyran (DCM) fluorophore, three of them conjugated with different phenylboronic acid fragments. By cellular uptake experiments, DLCB and DLAB showed enhanced cellular uptake abilities compared with DLN and DLO. These two effective phenylboronic acid fragments were then conjugated with SN-38 and the conjugates showed enhanced cellular uptake abilities by 3-fold or 7-fold compared with irinotecan. In summary, the strategy of introducing 4-carboxyphenylboronic acid and 3-amino-benzoxaborole groups shows great potential in drug delivery system. Moreover, the released linkers between boric acid and drugs deserve further studies.

Fluorescent glycoconjugates and their applications

Fluorescent glycoconjugates are discussed for their applications in biology in vitro, in cell assays and in animal models. Advantages and limitations are presented for each design using a fluorescent core conjugated with glycosides, or vice versa.

Selective turn-on near-infrared fluorescence probe for hypoxic tumor cell imaging

In this study, we designed a new selective turn on near-infrared fluorescence probe by conjugating (1-methyl-2-nitro-1H-imidazol-5-yl)methanol to DCPO with ether linkage for hypoxic tumor cell imaging.